1. Field
The present invention is concerned with novel liquid crystalline fluorocyclohexene-dioxane derivatives, liquid crystalline mixtures which contain such compounds, and the use of such compounds and mixtures in electro-optical devices.
2. Description
The optical properties of liquid crystals can be influenced by applied voltage, contributing to the use of liquid crystals primarily as dielectrics in display devices. Liquid crystals electro-optical devices are well-known to persons skilled in the art and can utilize various effects. Examples of such devices include cells having dynamic scattering, DAP cells ("deformed aligned phase"), guest/host cells, TN cells ("twisted nematic"), STN cells ("super twisted nematic"), SBE cells ("super birerefringence effect"), and OMI cells ("optical mode interference"). In displays having a high information content, actively controlled cells, such as TFT cells ("thin film transistor"), have joined passively controlled-multiplexed cells, and have recently become important to the industry. However, most common indicating devices are still based on the Schadt-Helfrich effect and have a twisted nematic structure.
To be useful, liquid crystal materials should have good chemical, photochemical and thermal stability, as well as good stability in electric fields. Further, they should have a suitable mesophase over the broadest range possible (for example, a nematic or a cholesteric phase for the cells referred to above). Nevertheless, liquid crystal materials should have a sufficiently low viscosity and should permit the production of mixtures having short response times, low threshold potentials, and high contrast. Further properties, such as the electrical conductivity, dielectric anisotropy, and optical anisotropy, must fulfill different requirements depending on the field of application and type of cell. For example, materials for twisted nematic cells should have a positive dielectric anisotropy which is as high as possible while simultaneously having a conductivity which is as low as possible. This latter property is of particular importance for TFT cells. Unfortunately, components having a high dielectric anisotropy typically yield mixtures having increased conductivity because of their improved capacity to dissolve ionic impurities. Accordingly, components having a dielectric anisotropy and a low conductivity are highly sought.
Compounds having a surprisingly high dielectric anisotropy and simultaneously a low conductivity as well as a relatively small optical anisotropy are provided by the present invention.